1. Field
The present technology relates to semiconductor devices.
2. Description of Related Art
The strong growth in demand for portable consumer electronics is driving the need for high-capacity storage devices. Non-volatile semiconductor memory devices, such as flash memory storage cards, are becoming widely used to meet the ever-growing demands on digital information storage and exchange. Their portability, versatility and rugged design, along with their high reliability and large capacity, have made such memory devices ideal for use in a wide variety of electronic devices, including for example digital cameras, digital music players, video game consoles, PDAs and cellular telephones.
While a wide variety of packaging configurations are known, flash memory storage cards may in general be fabricated as system-in-a-package (SiP) or multichip modules (MCM), where a plurality of die are mounted on a substrate in a stacked configuration. An edge view of a conventional semiconductor package 20 (without molding compound) is shown in prior art FIGS. 1 and 2. Typical packages include a plurality of semiconductor die mounted to a substrate 26. Three die 24, 26 and 28 are shown, but the package may include more or less die in further examples. Where the package is used as or within a memory card, one or more of the semiconductor die (e.g., die 24, 26) may be a non-volatile memory die, and one of the die (e.g., die 28) may be a controller die such as an ASIC. It is known to layer semiconductor die on top of each other either with an offset (prior art FIG. 1) or in a stacked configuration separated by a spacer layer 34 (prior art FIG. 2). Although not shown in FIGS. 1 and 2, the semiconductor die are formed with die bond pads on an upper surface of the die.
Substrate 28 may be formed of an electrically insulating core sandwiched between upper and lower conductive layers. The upper and/or lower conductive layers may be etched to form conductance patterns including electrical leads and contact pads. Wire bonds may be soldered between the die bond pads of the semiconductor die 22, 24, 26 and the contact pads of the substrate 28 to electrically couple the semiconductor die to the substrate. The electrical leads on the substrate in turn provide an electrical path between the die and a host device. Once electrical connections between the die and substrate are made, the assembly is then typically encased in a molding compound to provide a protective package.
As semiconductor packages are made smaller and power requirements increase, overheating of semiconductor die in the package is becoming a significant concern. In particular, present controller die are made with embedded high power transistors and other components which result in localized hot spots in the die. The increased heating significantly increases the aging of these components as well as affecting the normal operation and aging of the circuits in the immediate vicinity on the same die. Moreover, the highly non-uniform temperature distribution across the die introduces thermo-mechanical stresses in the die. As a result, the lifetime of the die decreases.
Localized hot spots may also be harmful to the operation of other die and components in a package including the controller die. This problem may be particularly acute in the case of a stacked-die memory package, where the controller die is stacked directly on top of the uppermost memory die (as shown in prior art FIGS. 1 and 2). Memory die are highly susceptible to temperature changes, and overheating of the attached controller die may cause performance degradation in one or more of the memory die in the die stack near the controller die. Packages containing these die may normally pass the standard screen tests, but then fail in an unacceptably short period of time in use by a customer or end-user.
One problem in identifying hot spots is that not all semiconductor die have hot spots in the same place or to the same degree. Each step in the multitude of fabrication steps of a semiconductor die has some degree of variation. Thus, for example, different electrical traces laid down within a semiconductor die may be more or less narrow from die to die. A narrow trace segment will result in higher resistance and higher temperatures through that segment. Semiconductor die may further include power regulators, which convert a supply voltage to a working voltage. Due to process variations, some of these regulators may be less efficient, and therefore run hotter than others.